Definition

Alternative Names

PT; Pro-time; Anticoagulant-prothrombin time; Clotting time: protime

How the Test is Performed

The health care provider uses a needle to take blood from one of your veins. The blood collects into an airtight container. You may be given a bandage to stop any bleeding. If you are taking a medicine called heparin, you will be watched for signs of bleeding.

The lab specialist will add chemicals to the blood sample and see how long it takes for the plasma to clot.

How to Prepare for the Test

Make sure your doctor knows about all the medicines you are taking. This including things you buy without a prescription such as over-the-counter medicines, herbs, and supplements. Your doctor may tell you to stop taking certain drugs before the test. For example, blood thinners can affect the results of this test.

Do not stop taking any medicine without first talking to your doctor.

How the Test will Feel

You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.

Why the Test is Performed

The most common reason to perform this test is to monitor your levels when you are taking a blood-thinning medicine called warfarin.

Version Info

David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.

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